P1084 疫情控制

Posted 2021-01-16 qdscwyy

Solution

二分答案, 尽量往上跳, 不能跳到根节点.
仍然能跳的拿出来.看剩下的点没有覆盖哪个?
贪心的分配一下.

Code

70

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
const int N = 50005;

int n, m;

struct Edge {
    int v, c; Edge* nxt;
    Edge(int _, int __, Edge* ___) :
            v(_), c(__), nxt(___) {}
} *head[N];
void AddEdge(int u, int v, int c) {
    head[u] = new Edge(v, c, head[u]);
    head[v] = new Edge(u, c, head[v]);
}

int f[N][18], p[N]; long long dis[N][18];

void dfs(int u, int fa, long long distan) {
    f[u][0] = fa, dis[u][0] = distan;
    for (int i = 1; i <= 17; i += 1) {
        f[u][i] = f[f[u][i - 1]][i - 1];
        dis[u][i] = dis[u][i - 1] + dis[f[u][i - 1]][i - 1];
    }
    for (auto edge = head[u]; edge; edge = edge->nxt) {
        if (edge->v != fa) 
            dfs(edge->v, u, edge->c);
    }
}
struct node {
    node() {} 
    long long rest; int id;
    node(int _id, int _r) :
        id(_id), rest(_r) {}
    bool operator < (const node& o) const {
        return rest < o.rest;
    }
} a[N], b[N];

int vis[N], used[N], R[N]; 
long long Min[N];
int A, B;

int Dfs(int u, int fa) {
    int f1 = true, noleaf = false;
    if (vis[u]) return true;
    for (auto edge = head[u]; edge; edge = edge->nxt) {
        if (edge->v == fa) continue;
        noleaf = true;
        if (not Dfs(edge->v, u)) {
            f1 = 0;
            if (u == 1)
                b[B++] = node(edge->v, edge->c);
            else return false;
        }
    }
    if (not noleaf) return false;
    return f1;
}

int check(long long lim) {
    int u, now; 
    long long num; 
    A = B = 0;
    for (int i = 1; i <= n; i += 1) vis[i] = 0;
    for (int i = 1; i <= n; i += 1) R[i] = 0;
    for (int i = 1; i <= m; i += 1) used[i] = 0;
    for (int i = 1; i <= m; i += 1) {
        u = p[i], num = 0;
        for (int j = 17; ~j; j -= 1)
            if (f[u][j] > 1 and num + dis[u][j] <= lim)
                num += dis[u][j], u = f[u][j];
        if (f[u][0] == 1 and num + dis[u][0] <= lim) {
            a[A++] = node(i, lim - num - dis[u][0]);
            if (not R[u] or a[A].rest < Min[u])
                Min[u] = a[A].rest, R[u] = i;
        } else vis[u] = 1;
    }
    if (Dfs(1, 0)) return true;
    sort(a, a + A);
    sort(b, b + B);
    now = 0, used[0] = 1;
    for (int i = 0; i < B; i += 1) {
        if (!used[R[b[i].id]]) {
            used[R[b[i].id]] = 1; continue;
        }
        while (now < A and (used[a[now].id] or a[now].rest < b[i].rest)) now += 1;
        if (now >= A) return false;
        used[a[now].id] = true;
    }
    return 1;
}

int main() {
    scanf("%d", &n);
    for (int i = 1, u, v, c; i < n; i += 1) {
        scanf("%d%d%d", &u, &v, &c);
        AddEdge(u, v, c);
    }
    dfs(1, 0, 0); 
    scanf("%d", &m);
    int l = 0, r = 5e5, mid;
    for (int i = 1; i <= m; i += 1) scanf("%d", &p[i]);
    while (l <= r) {
        mid = l + r >> 1;
        if (check(mid)) r = mid - 1;
        else l = mid + 1;
    }
    printf("%d
", l);
    return 0;
}